Turkish Journal of Veterinary and Animal Sciences
http://journals.tubitak.gov.tr/veterinary/
Research Article
Turk J Vet Anim Sci
(2015) 39: 615-620
© TÜBİTAK
doi:10.3906/vet-1502-42
Analysis of acid–base disorders in calves with lactic acidosis using a
classic model and strong ion approach
1,
2
Michal BEDNARSKI *, Robert KUPCZYŃSKI
Department of Epizootiology with Clinic of Birds and Exotic Animals, Faculty of Veterinary Medicine, Wroclaw University of
Environmental and Life Sciences, Wroclaw, Poland
2
Department of Environment Hygiene and Animal Welfare, Wroclaw University of Environmental and Life Sciences, Wroclaw, Poland
1
Received: 13.02.2015
Accepted/Published Online: 30.06.2015
Printed: 30.10.2015
Abstract: The objective of this study was to analyze the disorders of acid–base balance in calves with lactic acidosis using the classic
model and the strong ion approach. The study included 40 calves: group I was the control group (n = 20) and group II consisted of calves
with diarrhea and lactic acidosis (n = 20). The highest lactate concentration (5.49 ± 2.58 mmol/L) was documented in diarrheic calves.
The diarrheic calves presented with significantly lower pH, pCO2, and concentrations of HCO3– (P < 0.01), and with higher anion gap
(AG), strong ion difference (SID3, SID7), and strong ion gap (SIG) (P < 0.01) than the controls. In the group of diarrheic calves lactic
acid correlated with AG (r = 0.684, P < 0.01), SID3 (r = 0.718, P < 0.01), SID7 (r = 0.494, P = 0.03), and SIG (r = 0.561, P = 0.01). There
was a negative correlation between lactate and effective SID (SIDEff ) (r = –0.499, P = 0.02), and total plasma concentration of nonvolatile
buffers (ATot ) (r = –0.361, P = 0.04). The results indicated that in lactic acidosis there were specific disturbances with an increased
concentration of unmeasured strong ions.
Key words: Calves, diarrhea, acid–base balance, strong ion difference, lactic acidosis
1. Introduction
Neonatal calf diarrhea is a common disorder affecting
calves and is an important cause of economic losses. The
diarrhea of neonatal calves is usually associated with
bacterial (enterotoxigenic strains of E. coli), rotaviral,
and coronaviral infections and/or feeding factors (1,2).
Clinical signs of diarrhea include loose watery stools,
lack of appetite, and abdominal pain. This condition may
result in dehydration, acid–base disorders, and electrolyte
imbalances like metabolic acidosis, hyperkalemia,
prolonged malnutrition, hypoglycemia, and hypothermia
(3,4). The clinical status of an animal may further deteriorate
due to lactic acidosis, which has been reported in diarrheic
calves (5,6). Lactic acidosis is the result of elevated
concentrations of L-lactate or/and D-lactate in the blood
serum. L-lactate is produced by anaerobic metabolism due
to tissue hypoperfusion or low oxygen supply to the tissue,
while D-lactate is a byproduct of bacterial metabolism
(5–7). Although levels of L-lactate or/and D-lactate can be
elevated, only the nonstereospecific assay is routinely used
in clinical practice.
The interpretation of an acid–base balance is
traditionally based on changes in pH, bicarbonate
*Correspondence: [email protected]
concentration (HCO3–), base excess (BE), and anion gap
(AG) in plasma. This model characterizes four primary
acid–base disturbances (i.e. respiratory acidosis and
alkalosis, metabolic acidosis, and alkalosis) (8). The Stewart
model (strong ion model) represents an alternative method
of evaluation of acid–base status. This model is based on
three independent variables to determine the acid–base
balance: the strong ion difference (SID)—the difference
between all completely dissociated cations and anions;
the plasma partial pressure CO2 (pCO2), and the total
nonvolatile weak acid concentration, mainly inorganic
phosphate and albumin. The Stewart approach describes
six primary acid–base disturbances (i.e. respiratory
acidosis and alkalosis, strong ion acidosis and alkalosis,
and nonvolatile buffer ion acidosis and alkalosis). Although
the Stewart approach may give a better understanding of
the mechanisms that underlie an acid–base disorder, the
traditional methods are more convenient in daily practice
(4,8–10). Previous studies evaluated the use of two
models for description of acid–base disturbances in cases
of acute diarrhea, after intravenous fluid therapy or oral
rehydration therapy (3,4,11,12).
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BEDNARSKI and KUPCZYŃSKI / Turk J Vet Anim Sci
To the best of our knowledge none of the previous
studies analyzed the acid–base balance disorders using
the classic model and Stewart approach in calves with
lactic acidosis. In previous studies, the acid–base balance
of calves with lactic acidosis was determined using only
the classic model and only the association between lactate
(L-lactate or/and D-lactate) and the anion gap have been
investigated (8–10).
Therefore, the aim of this study was to compare the
classic model and the strong ion approach in calves with
lactic acidosis and prolonged diarrhea. We hypothesized
that acid–base analysis according to the strong ion
approach could result in important changes in diagnosis.
We also analyzed the association between lactate and
strong ion approach parameters in neonatal calves.
SID3 = [Na+] + [K+] – [ Cl–],
SID7 = ([Na+] + [K+] + [Mg2+ + [Ca2+]) – ([Cl–] +
[lactate]),
ATot = [albumin in g/dL] × [0.123 × pH – 0.631] + [P in
mmol/L × {pH – 0.469}],
SIDEff = 2.46 × 108 × pCO2/10 pH + ATot,
SIG = SID7 – SIDEff.
2.3. Statistical analysis
The results were subjected to statistical analysis with
Statistica ver. 10 software. The significance of intergroup
differences in the analyzed parameters was verified using
Duncan’s post-hoc test. The correlation analysis between
the serum lactate and anion gap and strong ion approach
parameters was carried out with Pearson’s test and simple
linear regression analysis.
2. Materials and methods
2.1. Study design
The study included 40 Holstein–Friesian calves, aged
between 7 and 21 days. Animals were housed in individual
calf boxes with straw bedding. Calves were fed two times
daily (at 0800 and 1700). Calves had ad libitum access
to water and were provided with hay and calf starter
concentrates. The calves were allocated to two groups:
group I (control group) consisted of healthy calves with
an appropriate acid–base balance (n = 20), and group II
consisted of calves (n = 20) with uncomplicated diarrhea
(yellow or gray-yellow stool and the absence of fever or
other clinical signs) lasting for 3–4 days and lactic acidosis
(concentration of serum lactate higher than 2.0 mmol/L).
All animals were subjected to clinical examination.
Dehydration status was determined by examining posture,
behavior, elasticity of skin, and the distance between
the eyeball and the palpebral conjunctiva in millimeters
(13). The protocol of the study was approved by the 2nd
Local Ethical Committee for Experiments on Animals in
Wroclaw (decision no. 23/2011).
2.2. Measurements and analyses
Heparinized jugular venous blood samples were collected
anaerobically, and acid–base parameters were determined
using a VetStat analyzer (Idexx, USA). The plasma
concentrations of sodium, potassium, chloride, calcium,
magnesium, inorganic phosphorous, albumin, and lactate
were measured with a Pentra 400 analyzer (Horiba ABX,
France). The anion gap (AG) was calculated as follows
(3,8):
AG = ([Na+] + [K+]) – ([HCO3–] + [Cl–])
In the strong ion model, the acid–base balance was
determined on the basis of the strong ion difference (SID),
total plasma concentration of nonvolatile buffers (ATot),
effective strong anion difference (SIDEff ), and strong ion
gap (SIG), calculated according to the following formulas
(8,9):
3. Results
All the calves with diarrhea presented with loose, yellow or
gray-yellow stools, and normal or slightly decreased rectal
body temperature (with a mean of 38.6 °C and a range of
37.8–38.9 °C). Animals from group II were weak, not able
to stand, but continued to nurse. Nine calves presented
with more than 5% dehydration.
The acid–base balance parameters of the study calves,
estimated with the Henderson–Hasselbach equation, are
presented in Table 1. The pH, plasma partial pressure
CO2 (pCO2), and concentrations of HCO3– of calves with
diarrhea were significantly lower (P < 0.01) than those
in the controls. The highest lactate concentration (5.49
mmol/L) was documented in calves from group II (animals
with chronic diarrhea). The calves from group II showed
significantly lower plasma concentrations of chloride and
phosphorus and significantly higher potassium. Diarrheic
animals had significantly higher anion gap values and
corrected anion gap values than healthy animals (P < 0.01).
The acid–base balance parameters of the strong ion
model are presented in Table 2. The diarrheic calves
presented with significantly higher SID3 (P < 0.01), SID7
(P < 0.01), and SIG (P < 0.01) values than animals from the
control group, whereas ATot (P < 0.01) and SIDEff (P < 0.01)
were significantly lower.
Table 3 shows the association between serum lactate
and the anion gap and parameters of the strong ion
approach for healthy and diarrheic calves. Data analysis
showed that the anion gap (r = 0.684, P < 0.01, Figure 1),
SID3 (r = 0.718, P < 0.01), SID7 (r = 0.494, P = 0.03), and
SIG (r = 561, P = 0.01, Figure 2) correlated with lactate
concentrations in group II (diarrheic calves). In addition,
there was a negative correlation between SIDEff and lactate
parameters in this group (r = –0.499, P = 0.02), and
between lactate and ATot (r = –0.361, P = 0.04). The anion
gap and the Stewart model parameters did not correlate
with blood serum lactate in healthy calves.
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Table 1. Mean values of acid–base balance parameters (classic model) and electrolytes level in calf blood.
Parameters
Group I (control)
Mean ± SD
Group II (diarrhea)
Mean ± SD
P-value
pH
7.38 ± 0.04
7.27 ± 0.08
<0.01
pCO2 kPa
5.93 ± 0.41
4.99 ± 0.61
<0.01
HCO3– (mmol/L)
26.65 ± 1.92
23.73 ± 1.85
<0.01
BE (mmol/L)
0.73 ± 1.12
–2.11 ± 2.01
<0.01
Na (mmol/L)
138.28 ± 2.9
136.55 ± 3.12
0.17
K (mmol/L)
4.69 ± 0.31
5.01 ± 0.54
<0.01
Cl (mmol/L)
102.99 ± 3.61
96.12 ± 4.15
<0.01
Albumins (g/L)
28.36 ± 1.94
25.13 ± 2.22
0.29
Lactate (mmol/L)
1.03 ± 0.40
5.49 ± 2.58
<0.01
Mg (mmol/L)
0.83 ± 0.11
0.84 ± 0.12
0.39
Ca (mmol/L)
2.27 ± 0.18
2.29 ± 0.31
0.40
P (mmol/L)
1.68 ± 0.21
1.46 ± 0.28
<0.01
AG (mmol/L)
13.24 ± 3.76
23.01 ± 3.15
<0.01
Table 2. Mean values of acid–base balance parameters of the strong ion approach.
Parameters
Group I (control)
Mean ± SD
Group II (diarrhea)
Mean ± SD
P-value
SID3 (mmol/L)
39.89 ± 2.32
46.90 ± 3.19
<0.01
SID7 (mmol/L)
41.39 ± 2.46
44.02 ± 3.75
<0.01
ATot (mmol/L)
11.83 ± 0.49
10.83 ± 0.99
<0.01
SIDEff (mmol/L)
36.27 ± 1.79
33.06 ± 1.93
<0.01
SIG (mmol/L)
2.40 ± 3.71
10.96 ± 3.11
<0.01
Table 3. Correlation coefficients between serum lactate concentrations and the anion
gap (AG) and the strong ion approach.
Parameters
Group I
(control)
Group II
(diarrhea)
AG
r
P-value
–0.032
0.894
0.684
<0.01
SID3
r
P-value
0.138
0.561
0.718
<0.01
SID7
r
P-value
–0.001
0.993
0.494
0.03
ATot
r
P-value
–0.334
0.149
–0.361
0.04
SIDEff
r
P-value
–0.054
0.820
–0.499
0.02
SIG
r
P-value
0.037
0.873
0.561
0.01
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Figure 1. Relationship between the anion gap (AG) and serum
lactate with the least squares line for group II (calves with
diarrhea). y = 0.34 x +1.25, r = 0.684, n = 20, P < 0.01.
Figure 2. Relationship between SIG and serum lactate with the
least squares line for group II (calves with diarrhea). y = 0.32 x
+2.29, r = 0.561, n = 20, P < 0.01.
4. Discussion
The analysis of gasometrical and biochemical parameters
in the blood is an important tool in evaluating acid–base
disturbances. Metabolic acidosis is diagnosed based on
decreases in pH, blood bicarbonate, and base excess,
which are accompanied by an increased anion gap. Blood
electrolytes and serum organic acids may be helpful in
diagnosing the type of acidosis (4,8,9). One of them is
lactic acidosis. This specific type of acidosis is associated
with high lactate concentrations found in the blood (6,9).
The analysis based on the classic model of blood pH and
other acid–base balance parameters of calves with diarrhea
indicated a mild metabolic acidosis (3,14,15). This type of
disorder was considered due to a reduction in pH (reference
value: 7.32–7.44) and a negative value of BE (1,16). Our
results correspond to commonly reported findings of
decreased HCO–3 and chloride, and increased potassium.
However, the concentrations of HCO3– and BE indicated
the beginning of a compensation process. The calves with
diarrhea (group II) presented with significantly lower
concentrations of chloride than the controls. Contrary to
the calves from group II, in acute diarrhea hyponatremia
(Na+ is usually below reference value: 132–152 mmol/L)
and hyperchloremia or normochloremia (reference value:
97–111 mmol/L) are observed (12,16). However, previous
studies documented a decrease in plasma Cl– concentrations
of diarrheic calves (17), especially in animals with severe
diarrhea (18). The etiology of hypochloremia observed
in our calves might be heterogeneous, i.e. resulting from
many alimentary disorders, abomasal atony, vomiting, or
lack of chloride reabsorption in the distal segment of the
alimentary tract (19). The decrease in Cl– concentration may
also represent a compensatory mechanism for prolonged
acidosis associated with high concentrations of organic
anions, like elevated levels of lactate (20,21).
The levels of lactate in healthy animals were consistent
with typical values for calves, which vary between 0.5 and
2.0 mmol/L (5). The mean concentration of lactate in
the group with prolonged diarrhea (5.49 mmol/L) was
typical for advance lactic acidosis (>4.0 mmol/L) (5,6,21).
However, the lactate concentration measured using a
nonstereospecific assay could not explain whether the
examined calves had elevated blood concentrations of
L-lactate or/and D-lactate (10).
Anion gap values obtained for the control group were
consistent with AG values in the literature (9,10,16,19).
The calves with diarrhea presented significantly higher
anion gaps than the controls. Elevated anion gap acidosis
in calves with alimentary disorders generally was due to
overproduction of organic acids. The most common anions
found in such cases were lactate and keto acids (5,6,10).
The results of our study indicate that AG correlated with
lactate concentrations in serum only in the group of calves
with diarrhea. This finding was consistent with a previous
finding that DL-lactate was significantly correlated with
AG in diarrheic neonatal calves (10). This association
was not observed in the group of healthy calves. A study
by Ewaschuk et al. (10) indicated that AG significantly
correlated with D-lactate, while another study (9) showed
a correlation with serum L-lactate concentrations.
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The analysis based on the strong ion model of animals
from group II revealed elevated values of SID3 and SID7,
accompanied by a decrease in ATot and SIDEff. These findings
correspond to a compensated acid–base disorder with a
shift towards the alkaline side. Elevated SID parameters
indicated a strong anion alkalosis, partly caused by lower
concentrations of chloride. SID alkalosis was observed in
some calves with diarrhea by Gomez et al. (3), assuming
the values 38–46 mmol/L provided by Constable (12) as
normal values for calves. Moreover, in group II, SID3 was
higher than in the control group. This finding confirmed
the significant influence of lactate concentration on the
strong ion difference (3,12). Decreased ATot indicated a
nonvolatile buffer ion alkalosis, most probably due to
decreases in plasma concentrations of phosphate and
albumin (12). Elevated SIG points to a difference between
the sum of all strong cation concentrations and the sum
of all measured anion concentrations (chloride, lactate,
albumins, phosphate, and HCO3–), resulting from the
presence of elevated concentrations of unmeasured strong
ions, such as fatty acids, keto acids, and sulfate (20,22,23).
SIG estimated for healthy calves by Constable is from 3
to –3 mmol/L (3,12). The described disturbance in the
strong ion approach was contrary to a previous finding
in calves with diarrhea, where ATot was elevated, while
SIG was significantly lower than the reference value (3).
Our study showed that the parameters of the strong ion
approach (SID and SIG) correlated with concentrations of
lactate similarly to AG. Moreover, the observed negative
correlation between ATot, SIDEff, and lactate indicated a
compensation of lactic acidosis, by decreases in nonvolatile
buffers and bicarbonate concentrations. However, the
described associations were observed only in diarrheic
calves. These results indicated that in lactic acidosis there
were specific disturbances with increased concentrations
of unmeasured strong ions detected by the calculation
of the SIG. The classic model in this case was useful for
describing and classifying acid–base disorders, whereas
the strong ion approach (SID, ATot, and SIG) was more
useful for quantifying and explaining these disorders.
Acidosis in calves with diarrhea is due predominantly
to a strong ion acidosis in response to hyponatremia
accompanied by normochloremia or hyperchloremia
(3,4,12). Therefore, a highly effective SID solution (sodium
bicarbonate) is used to correct this acid–base disturbance,
the strong ion acidosis (decrease of SID). Our data suggest
that the presented cases of diarrhea can be treated with an
isotonic solution of NaCl, except for treatment of calves
with hyperkalemia. In the case of lactic acidosis, the liver
metabolizes the circulating lactate (21).
In conclusion, the characterization of acid–base
disturbances in cases of lactic acidosis in prolonged
diarrhea showed that the classic model has some
limitations. Using the strong ion approach, we found the
presence of more than one acid–base disturbance and
increased concentrations of unmeasured strong ions
detected by the calculation of the SIG.
Acknowledgment
This study was performed within the research project No.
N N308 575439 funded by the Polish Ministry of Science
and Higher Education.
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